# I want to mechanically detect when an egg-timer runs out - ideas?

• Misc.
• some bloke
In summary, the conversation discusses ways to mechanically detect when an egg timer has run out in order to create a classic egg-timer with an alarm. The initial idea of using water as a sensor is debunked, and other options such as swinging a mechanism or using a viscous fluid are considered. The final goal is to create a mechanically detectable egg timer without using electricity. The conversation ends with a suggestion to suspend the egg timer and use a sensing method to detect the change in the center of gravity as the sand flows to the lower chamber. The conversation concludes with a note to share the final result.

#### some bloke

TL;DR Summary
I'm trying to design an egg timer which will actually sound an alarm when it goes off.
Hi everyone,

I'm trying to come up with a method for designing a classic egg-timer (falling sand) which will sound an alarm when it goes off. The alarm itself is going to be some contraption akin to a Rube-Goldberg machine, which I can design after I work out how to mechanically detect when an egg timer has run out. Making noise isn't the problem here -detecting when an egg timer runs out is!

My first thought on this was to have the egg timer suspended in a tube of water, and I initially thought that it would float higher in the water as the sand poured down, as its center of gravity would change. I have since worked out that this wouldn't happen - the mass of the egg timer would not change, so it wouldn't change how high it floats in the water - thus my first thought is foiled from the off!

I am after ideas on how to mechanically detect an egg-timer running out. One option would be to put something in the path of the falling sand, so that when the sand stops flowing it would swing back to a position. Another option I am looking at is making an egg timer in two pieces, so that as one side fills up its weight can trigger a mechanism.

I am also considering how to make this in a different manner entirely - my goal is a mechanical timer which sounds an alarm when it is finished. I could use a viscous fluid and have something sink through it, or any other means of giving a reproducible time effect. If I can, I want it to be adjustable on time, but I'm not getting my hopes up on that one! Just a mechanically detectable egg timer type thing would be ideal! And no electricity!

Do you have any ideas that would fit the bill here? Any suggestions I can look into?

Quite interesting challenge

2milehi
A standard sand (often salt) egg timer
suspend from a string attached to the periphery of the top edge

1) As the sand flows to the lower chamber the center of gravity will change.
2) The angle of the egg timer will then vary to keep the center of gravity directly below the support point.
3) Use the sensing of your choice to detect the horizontal movement of the bottom edge of the timer.
3a) Following edit somehow didn't get in this post when created: (Perhaps by pushing a marble off a platform down a ramp to increase available energy.)

Have Fun! ...and be sure to show us the result!

Cheers,
Tom

Last edited:
dlgoff and berkeman

## 1. How can I mechanically detect when an egg-timer runs out?

One idea is to use a mechanical switch that is triggered by the movement of the egg-timer's dial or knob when it reaches zero. Another idea is to use a lever or weight system that is activated when the egg-timer's internal mechanism finishes counting down.

## 2. What materials do I need to create a mechanical egg-timer detector?

The materials needed will depend on the specific design and mechanism you choose. Generally, you will need some type of mechanical switch, such as a microswitch or reed switch, as well as a power source, wires, and possibly additional components like gears or levers.

## 3. Can I use a digital egg-timer for this project?

Yes, you can still use a digital egg-timer with a mechanical detector. Instead of detecting the movement of the dial or knob, the mechanical switch could be triggered when the digital display reaches zero.

## 4. Are there any safety concerns with using a mechanical egg-timer detector?

As with any DIY project, it is important to take safety precautions and handle materials and tools carefully. If using electronic components, make sure to follow proper wiring and power supply guidelines to avoid any potential hazards.

## 5. Can I modify this project for other uses besides an egg-timer?

Yes, the concept of a mechanical detector can be applied to other countdown or timing devices. With some modifications, it could also be used for non-timing purposes, such as detecting when a door or window is opened or closed.